Cards

Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.

Setup code

To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:

library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)

plotly_widget <- plot_ly(x = diamonds$cut) %>%
  config(displayModeBar = FALSE) %>%
  layout(margin = list(t = 0, b = 0, l = 0, r = 0))

leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
  leaflet(options = .) %>%
  addTiles()

Shiny usage

Cards work equally well in Shiny. In the examples below, replace plotly_widget with plotlyOutput() and leaflet_widget with leafletOutput() to adapt them for Shiny server-rendered plots/maps.

Hello `card()`

A card() is designed to handle any number of “known” card items (e.g., card_header(), card_body(), etc) as unnamed arguments (i.e., children). As we’ll see shortly, card() also has some useful named arguments (e.g., full_screen, height, etc).

At their core, card() and card items are just an HTML div() with a special Bootstrap class, so you can use Bootstrap’s utility classes to customize things like colors, text, borders, etc.

card(
  card_header(
    class = "bg-dark",
    "A header"
  ),
  card_body(
    markdown("Some text with a [link](https://github.com)")
  )
)

A header

Some text with a link

Implicit `card_body()`

If you find yourself using card_body() without changing any of its defaults, consider dropping it altogether since any direct children of card() that aren’t “known” card() items, are wrapped together into an implicit card_body() call.¹ For example, the code to the right generates HTML that is identical to the previous example:

card(
  card_header(
    class = "bg-dark",
    "A header"
  ),
  markdown("Some text with a [link](https://github.com).")
)

A header

Some text with a link.

Restricting growth

By default, a card()’s size grows to accommodate the size of it’s contents. Thus, if a card_body() contains a large amount of text, tables, etc., you may want to specify a height or max_height. That said, when laying out multiple cards, it’s likely best not to specify height on the card(), and instead, let the layout determine the height layout_column_wrap().

Although scrolling is convenient for reducing the amount of space required to park lots of content, it can also be a nuisance to the user. To help reduce the need for scrolling, consider pairing scrolling with full_screen = TRUE (which adds an icon to expand the card’s size to the browser window). Notice how, when the card is expanded to full-screen, max_height/height won’t effect the full-screen size of the card.

card(
  max_height = 250,
  full_screen = TRUE,
  card_header(
    "A long, scrolling, description"
  ),
  lorem::ipsum(paragraphs = 3, sentences = 5)
)

A long, scrolling, description

Sit maecenas convallis urna etiam sodales sapien, proin dictum dapibus sem? Habitasse platea quis est in magna quisque fringilla parturient rutrum vestibulum facilisis. Et quisque vestibulum, ullamcorper tincidunt condimentum porta eleifend conubia primis, sagittis semper ligula! Habitasse mus vel rutrum rhoncus; volutpat vel consequat mi lacus tellus mus tristique! Dapibus magnis at.

Consectetur faucibus convallis montes suscipit quis – scelerisque nascetur nullam lacus! Tempor litora mattis hendrerit sodales vel nisi. Duis sem malesuada a arcu quis consequat purus mus dignissim, varius velit dictumst! Sodales luctus sed, rutrum scelerisque mus dictum! Semper imperdiet condimentum scelerisque ridiculus tristique auctor volutpat neque porttitor – eleifend magna, maecenas arcu fermentum.

Ipsum quis luctus dictumst praesent dapibus primis, varius vestibulum pharetra imperdiet. Cras quisque est eget lobortis per: eget vehicula placerat erat mollis? Primis urna eu scelerisque eu dui: senectus, pharetra urna sociis! Mattis curabitur ornare natoque id cum blandit mauris iaculis nisl. Na nisl.

Filling outputs

A card()’s default behavior is optimized for facilitating filling layouts. More specifically, if a fill item (e.g., plotly_widget), appears as a direct child of a card_body(), it resizes to fit the card()s specified height. This means, by specifying height = 250 we’ve effectively shrunk the plot’s height from its default of 400 down to about 200 pixels. And, when expanded to full_screen, the plot grows to match the card()’s new size.

card(
  height = 250,
  full_screen = TRUE,
  card_header("A filling plot"),
  card_body(plotly_widget)
)

A filling plot

Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny output bindings (e.g, plotOutput(), imageOutput(), etc) are fill items by default, so this behavior “just works” in those scenarios. And, in some of these situations, it’s helpful to remove card_body()’s padding, which can be done via spacing & alignment utility classes.

card(
  height = 275,
  full_screen = TRUE,
  card_header("A filling map"),
  card_body(
    class = "p-0",
    leaflet_widget
  ),
  card_footer(
    class = "fs-6",
    "Copyright 2023 RStudio, PBC"
  )
)

A filling map

Fill item(s) aren’t limited in how much they grow and shrink, which can be problematic when a card becomes very small. To work around this, consider adding a min_height on the card_body() container. For example, try using the handle on the lower-right portion of this card example to make the card taller/smaller.

This interactive example is a bit contrived in that we’re using CSS resize to demonstrate how to make plots that don’t shrink beyond a certain point, but this concept becomes quite useful when implementing page-level filling layouts (i.e., page_fillable()) with multiple cards.

card(
  height = 300,
  style = "resize:vertical;",
  card_header("Plots that grow but don't shrink"),
  card_body(
    min_height = 250,
    plotly_widget,
    plotly_widget
  )
)

Plots that grow but don't shrink

Troubleshooting fill

As you’ll learn more about in filling layouts, a fill item loses its ability to fill when wrapped in additional UI element that isn’t a fillable container. To fix the situation, use as_fill_carrier() to allow the additional element to carry the potential to fill from the card_body() down to the fill item.

Multiple `card_body()`

A card() can have multiple card_body()s, which is especially useful for:

Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
Allowing each card_body() to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g., min_height).

For example, when pairing filling output with scrolling content, you may want min_height on the filling output since the scrolling content will force it to shrink:

card(
  height = 375,
  full_screen = TRUE,
  card_header(
    "Filling plot, scrolling description"
  ),
  card_body(
    min_height = 200,
    plotly_widget
  ),
  card_body(
    class = "lead container",
    lorem::ipsum(paragraphs = 10, sentences = 5)
  )
)

Filling plot, scrolling description

Ipsum fringilla leo, nunc egestas taciti enim nostra torquent vivamus imperdiet felis magnis fusce. Tempus tempor primis tortor volutpat molestie et proin taciti congue leo cras. At integer aliquam in integer vestibulum imperdiet. Parturient nam bibendum ridiculus ligula malesuada natoque condimentum tempus facilisi aliquam pellentesque. Vitae purus natoque erat placerat porttitor suspendisse.

Sit in eget erat pulvinar malesuada aptent. Erat aliquet tincidunt vehicula faucibus tristique. Fames ridiculus porta odio aliquet, faucibus orci gravida nam; nulla himenaeos a placerat! Eu posuere purus interdum, dictum, tincidunt taciti dignissim ac pellentesque etiam pharetra. Natoque habitant iaculis fringilla dictum posuere lectus: lobortis aliquet maecenas ornare nisl aliquam laoreet pulvinar facilisi!

Adipiscing pellentesque nibh urna rutrum vulputate montes inceptos praesent et. Magna nullam nostra risus penatibus volutpat, condimentum gravida. Auctor nisl id feugiat erat ultricies nam sociis! Eu aliquam magnis tortor – nullam ultricies natoque. Lectus varius ornare pulvinar aliquet, hac, auctor ut tempus vivamus, eu etiam nisl commodo vivamus eu potenti sodales lacus vivamus!

Amet dictum accumsan et lectus feugiat morbi. Cum natoque purus ullamcorper bibendum pretium sed sapien proin laoreet. Varius risus eros dictum nulla aptent! Urna arcu vehicula accumsan nullam pulvinar tempor mus iaculis, mollis nisi. Iaculis leo libero penatibus imperdiet sollicitudin est magna mollis metus phasellus mattis in felis at dictum nullam nam mauris posuere mattis maecenas phasellus felis magna.

Elit vivamus diam: quis, dis volutpat semper risus ad vitae. Sociis tristique nascetur nostra neque suscipit: tortor faucibus condimentum venenatis. Dignissim tempor sapien eu netus neque pharetra ultricies, mauris mi donec. Eget in cursus diam magna torquent, nam donec: massa pretium! Na pretium.

Sit curabitur habitant odio ultricies hac, euismod dictumst viverra a. Per nascetur laoreet cursus lobortis metus diam – penatibus, iaculis vehicula conubia donec vulputate! Lacinia suspendisse vestibulum montes eu justo. A aenean porttitor pretium; cum ad nam hendrerit lectus enim purus. Aliquam commodo cursus taciti porta cubilia, justo molestie dui; bibendum massa accumsan; conubia congue.

Adipiscing ridiculus laoreet varius nisl posuere vehicula. Suscipit habitasse, dapibus integer volutpat enim mauris inceptos accumsan posuere. Condimentum tempor himenaeos quisque fames massa aenean; montes pretium blandit. Malesuada etiam risus parturient torquent venenatis! Lacus nisi tincidunt varius eu dapibus risus hendrerit, sem nibh tristique fringilla non – posuere sapien dis id?

Ipsum turpis erat egestas quisque fringilla erat orci lacinia vel vestibulum. Integer interdum imperdiet pulvinar molestie enim, felis luctus dis justo mi quisque! Congue aliquam risus eleifend libero non justo imperdiet massa. Vestibulum mauris tristique integer facilisis magnis a. Nisi purus malesuada mattis volutpat orci dignissim habitant luctus.

Lorem tempor, ad taciti justo mattis pretium odio eu at. Diam eget penatibus, hac nascetur pellentesque dapibus aptent risus. Augue montes netus mi sociosqu porta purus vulputate velit suspendisse? Mattis risus convallis: bibendum cum, orci dictumst curae pulvinar posuere! Justo habitasse posuere diam justo nam phasellus tincidunt a blandit fames curabitur purus, velit nisi sodales blandit dui magna?

Elit volutpat vel mollis potenti curabitur auctor sagittis, platea integer accumsan. Nunc vulputate nunc, per habitant mus tortor ligula laoreet vehicula curae dapibus. Integer sem tempus pellentesque luctus sagittis nascetur primis curabitur est. Felis laoreet molestie – dignissim duis vivamus cursus pretium. Eu id congue suspendisse sed eu ullamcorper, dictumst placerat fusce; neque egestas; metus nascetur bibendum porta!

Also, when the content has a fixed size, and should not be allowed to scroll, set fill = FALSE:

card(
  height = 350,
  full_screen = TRUE,
  card_header(
    "Filling plot, short description"
  ),
  plotly_widget,
  card_body(
    fill = FALSE,
    card_title("A subtitle"),
    p(class = "text-muted", "And a caption")
  )
)

Filling plot, short description

A subtitle

And a caption

Multiple columns

As you’ll learn in column-based layouts, layout_column_wrap() is great for multi-column layouts that are responsive and accommodate for filling output. Here we have an equal-width 2-column layout using width = 1/2, but it’s also possible to have varying column widths.

card(
  height = 350,
  full_screen = TRUE,
  card_header("A multi-column filling layout"),
  card_body(
    min_height = 200,
    layout_column_wrap(
      width = 1/2,
      plotOutput("p1"),
      plotOutput("p2")
    )
  ),
  lorem::ipsum(paragraphs = 3, sentences = 5)
)

A multi-column filling layout

Amet et class facilisi quis sed potenti dignissim aenean natoque sociis. Tempor conubia, sed, curae aptent vitae molestie commodo elementum. Eu mus vivamus cubilia cursus massa sociis curae. Congue massa montes semper, in luctus nam. Natoque ridiculus senectus potenti penatibus aliquet conubia tincidunt erat sociis ante enim.

Ipsum malesuada vulputate dictumst tempus cubilia habitant conubia varius. Id curae velit placerat aliquam lectus sem suspendisse auctor. Neque ultrices aenean – eu tempor lobortis sagittis, platea proin vel cum vulputate inceptos torquent. Iaculis litora: sem litora vestibulum penatibus euismod rutrum euismod nunc aliquam mollis vel. Na vel.

Elit nisi bibendum mus cras dignissim phasellus malesuada. Dictum praesent interdum, facilisi iaculis litora curabitur ornare. Vulputate interdum maecenas sociis sapien tortor condimentum luctus vulputate donec. Faucibus senectus magna id sollicitudin hendrerit – hac facilisis sociosqu pellentesque. Vitae nascetur primis cras torquent lectus felis ornare, lacinia, facilisi libero.

Multiple cards

layout_column_wrap() is especially nice for laying out multiple cards since each card in a particular row will have the same height (by default). Learn more in column-based layouts.

layout_column_wrap(
  width = 1/2,
  height = 300,
  card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
  card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)

A filling plot

A filling map

Multiple tabs

navset_card_tab() and navset_card_pill() make it possible to create cards with multiple tabs or pills. These functions have the same full_screen capabilities as normal card()s as well some other options like title (since there is no natural place for a card_header() to be used). Note that, each nav_panel() object is similar to a card(). That is, if the direct children aren’t already card items (e.g., card_title()), they get implicitly wrapped in a card_body().

library(leaflet)
navset_card_tab(
  height = 450,
  full_screen = TRUE,
  title = "HTML Widgets",
  nav_panel(
    "Plotly",
    card_title("A plotly plot"),
    plotly_widget
  ),
  nav_panel(
    "Leaflet",
    card_title("A leaflet plot"),
    leaflet_widget
  ),
  nav_panel(
    shiny::icon("circle-info"),
    markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
  )
)

HTML Widgets

Plotly
Leaflet

A plotly plot

A leaflet plot

Learn more about htmlwidgets

Sidebars

As you’ll learn more about in sidebar layouts, layout_sidebar() just works when placed inside in a card(). In this case, if you want fill items (e.g., plotly_widget) to still fill the card like we’ve seen before, you’ll need to set fillable = TRUE in layout_sidebar().

card(
  height = 300,
  full_screen = TRUE,
  card_header("A sidebar layout inside a card"),
  layout_sidebar(
    fillable = TRUE,
    sidebar = sidebar(
      actionButton("btn", "A button")
    ),
    plotly_widget
  )
)

A sidebar layout inside a card

Static images

card_image() makes it easy to embed static (i.e., pre-generated) images into a card. Provide a URL to href to make it clickable. In the case of multiple card_image()s, consider laying them out in multiple cards with layout_column_wrap() to produce a grid of clickable thumbnails.

card(
  height = 300,
  full_screen = TRUE,
  card_image(
    file = "shiny-hex.svg",
    href = "https://github.com/rstudio/shiny"
  ),
  card_body(
    fill = FALSE,
    card_title("Shiny for R"),
    p(
      class = "fw-light text-muted",
      "Brought to you by RStudio."
    )
  )
)

Shiny for R

Brought to you by RStudio.

Flexbox

Both card() and card_body() default to fillable = TRUE (that is, they are CSS flexbox containers), which works wonders for facilitating filling outputs, but it also leads to surprising behavior with inline tags (e.g., actionButton(), span(), strings, etc). Specifically, each inline tag is placed on a new line, but in a “normal” layout flow (fillable = FALSE), inline tags render inline.

card(
  card_body(
    fillable = TRUE,
    "Here's some", tags$i("inline"), "text",
    actionButton("btn1", "A button")
  ),
  card_body(
    fillable = FALSE,
    "Here's some", tags$i("inline"), "text",
    actionButton("btn2", "A button")
  )
)

Here's some inline text

That said, sometimes working in a flexbox layout is quite useful, even when working with inline tags. Here we leverage flexbox’s gap property to control the spacing between a plot, a (full-width) button, and paragraph. Note that, by using markdown() for the paragraph, it wraps the results in a <p> tag, which means the contents of the paragraph are not longer subject to flexbox layout. If we wanted, we could do something similar to render the actionButton() inline by wrapping it in a div().

card(
  height = 325, full_screen = TRUE,
  card_header("A plot with an action links"),
  card_body(
    class = "gap-2 container",
    plotly_widget,
    actionButton(
      "go_btn", "Action button",
      class = "btn-primary rounded-0"
    ),
    markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
  )
)

A plot with an action links

Here's a simple hyperlink.

In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.

card(
  height = 300, full_screen = TRUE,
  card_header(
    class = "d-flex justify-content-between",
    "Centered plot",
    checkboxInput("check", " Check me", TRUE)
  ),
  card_body(
    class = "align-items-center",
    plotOutput("id", width = "75%")
  )
)

Centered plot

Check me

Shiny

Since this article is statically rendered, the examples here use statically rendered content/widgets, but the same card() functionality works for dynamically rendered content via Shiny (e.g., plotOutput(), plotlyOutput(), etc).

An additional benefit that comes with using shiny is the ability to use getCurrentOutputInfo() to render new/different content when the output container becomes large enough, which is particularly useful with card(full_screen = T, ...). For example, you may want additional captions/labels when a plot is large, additional controls on a table, etc (see the value boxes article for a clever use of this).

# UI logic
ui <- page_fluid(
  card(
    max_height = 200,
    full_screen = TRUE,
    card_header("A dynamically rendered plot"),
    plotOutput("plot_id")
  )
)

# Server logic
server <- function(input, output, session) {
  output$plot_id <- renderPlot({
    info <- getCurrentOutputInfo()
    if (info$height() > 600) {
      # code for "large" plot
    } else {
      # code for "small" plot
    }
  })
}

shinyApp(ui, server)

Appendix

The following CSS is used to give plotOutput() a background color; it’s necessary here because this documentation page is not actually hooked up to a Shiny app, so we can’t show a real plot.

.shiny-plot-output {
  background-color: #216B7288;
  height: 400px;
  width: 100%;
}